上学时老师总是教我们要保护环境，也就是保护人类。如今，环境污染严重，我家乡的河流变脏了，也没有人下去玩耍了。

When we go to school, teachers always teach us to protect the environment, so as to protect human being. Today, the environment has been polluted badly. The river in my hometown becomes dirty and no one will play there. We can barely see birds flying in the sky. The change of environment needs us to improve. 
上学时老师总是教我们要保护环境，也就是保护人类。如今，环境污染严重，我家乡的河流变脏了，也没有人下去玩耍了。我们几乎看不到鸟儿在天上飞。环境的变化需要我们去改善。